Targeting of SNAP-23 and SNAP-25 in polarized epithelial cells.
SNAP-23 is the ubiquitously expressed homologue of the neuronal SNAP-25, which functions in synaptic vesicle fusion. We have investigated the subcellular localization of SNAP-23 in polarized epithelial cells. In hepatocyte-derived HepG2 cells and in Madin-Darby canine kidney (MDCK) cells, the majority of SNAP-23 was present at both the basolateral and apical plasma membrane domains with little intracellular localization. This suggests that SNAP-23 does not function in intracellular fusion events but rather as a general plasma membrane t-SNARE. Canine SNAP-23 is efficiently cleaved by the botulinum neurotoxin E, suggesting that it is the toxin-sensitive factor previously found to be involved in plasma membrane fusion in MDCK cells. The localization of SNAP-25 in transfected MDCK cells was studied for comparison and was found to be identical to SNAP-23 with the exception that SNAP-25 was transported to the primary cilia protruding from the apical plasma membrane, which suggests that subtle differences in the targeting signals of both proteins exist. In contrast to its behavior in neurons, the distribution of SNAP-25 in MDCK cells remained unaltered by treatment with dibutyryl cAMP or forskolin, which, however, caused an increased growth of the primary cilia. Finally, we found that SNAP-23/25 and syntaxin 1A, when co-expressed in MDCK cells, do not stably interact with each other but are independently targeted to the plasma membrane and lysosomes, respectively.
Low
S H
SH
Department of Anatomy, Cardiovascular Research Institute, University of California, San Francisco, California 94143-0452, USA.
Roche
P A
PA
Anderson
H A
HA
van Ijzendoorn
S C
SC
Zhang
M
M
Mostov
K E
KE
Weimbs
T
T
D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D001905:Botulinum Toxins / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D008561:Membrane Fusion; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D014162:Transfection; D014407:Tumor Cells, Cultured
D000954:Antigens, Surface; D002352:Carrier Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; C100493:SNAP23 protein, human; C494208:SNAP25 protein, human; C494212:STX1A protein, human; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D001905:Botulinum Toxins; C096326:botulinum toxin type E